Editorial Type:
Surgery

In vitro evaluation of five canine tibial plateau leveling methods

Blake Eason Hildreth III Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606.

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 DVM
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Denis J. Marcellin-Little Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606.

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Simon C. Roe Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606.

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Ola L. A. Harrysson Department of Industrial Engineering, College of Engineering, North Carolina State University, Raleigh, NC 27606.

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DOI:
https://doi.org/10.2460/ajvr.67.4.693
Volume/Issue:
Volume 67: Issue 4
Online Publication Date:
01 Apr 2006
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Abstract

Objective—To compare application time, accuracy of tibial plateau slope (TPS) correction, presence and magnitude of rotational and angular deformities, and mechanical properties of 5 canine tibial plateau leveling methods.

Sample Population—27 canine tibial replicas created by rapid prototyping methods.

Procedure—The application time, accuracy of TPS correction, presence and magnitude of rotational and angular deformation, and construct axial stiffness of 3 internal fixation methods (tibial plateau leveling osteotomy, tibial wedge osteotomy, and chevron wedge osteotomy [CWO]) and 2 external skeletal fixation (ESF) methods (hinged hybrid circular external fixation and wedge osteotomy linear fixation [WOLF]) were assessed.

Results—Mean bone model axial stiffness did not differ among methods. Mean application time was more rapid for WOLF than for other methods. Mean TPSs did not differ from our 5° target and were lower for ESF methods, compared with internal fixation methods. Mean postoperative rotational malalignment did not differ from our target or among groups. Mean postoperative medio-lateral angulation did not differ from our target, except for CWO. Internal fixation methods lead to axially stiffer constructs than ESF methods. Reuse of ESF frames did not lead to a decrease in axial stiffness.

Conclusions and Clinical Relevance—The 5 tibial plateau leveling methods had acceptable geometric and mechanical properties. External skeletal fixation methods were more accurate as a result of precise data available for determining the exact magnitude of correction required to achieve a 5° TPS.

Abstract

Objective—To compare application time, accuracy of tibial plateau slope (TPS) correction, presence and magnitude of rotational and angular deformities, and mechanical properties of 5 canine tibial plateau leveling methods.

Sample Population—27 canine tibial replicas created by rapid prototyping methods.

Procedure—The application time, accuracy of TPS correction, presence and magnitude of rotational and angular deformation, and construct axial stiffness of 3 internal fixation methods (tibial plateau leveling osteotomy, tibial wedge osteotomy, and chevron wedge osteotomy [CWO]) and 2 external skeletal fixation (ESF) methods (hinged hybrid circular external fixation and wedge osteotomy linear fixation [WOLF]) were assessed.

Results—Mean bone model axial stiffness did not differ among methods. Mean application time was more rapid for WOLF than for other methods. Mean TPSs did not differ from our 5° target and were lower for ESF methods, compared with internal fixation methods. Mean postoperative rotational malalignment did not differ from our target or among groups. Mean postoperative medio-lateral angulation did not differ from our target, except for CWO. Internal fixation methods lead to axially stiffer constructs than ESF methods. Reuse of ESF frames did not lead to a decrease in axial stiffness.

Conclusions and Clinical Relevance—The 5 tibial plateau leveling methods had acceptable geometric and mechanical properties. External skeletal fixation methods were more accurate as a result of precise data available for determining the exact magnitude of correction required to achieve a 5° TPS.

Disease of the CCL is among the most common orthopedic problems and the leading cause of degenerative joint disease of the canine stifle joint. Surgical stabilization is recommended for most affected dogs.1 Cranialto-caudal angulation of the tibial plateau relative to the functional axis (ie, TPS) influences stress on the CCL during locomotion.2 The craniad force placed on the CCL increases with an increasing TPS.3 Clinically, TPS appears larger in some dogs with CCL disease, but not in others, suggesting a link between increased craniad forces and subsequent CCL disease.4,5 In cruciate-deficient stifles, craniad forces lead to cranial proximal tibial translation in relation to the femoral condyles, representing cranial drawer or cranial tibial thrust.6 Several surgical procedures are used to decrease TPS in dogs with CCL disease, therefore decreasing cranial tibial thrust.7–9 These corrective modalities rely on acute, intraoperative sliding, rotational, or closing wedge osteotomies and plate fixation and include the TPLO8 and TWO.9 The TPLO was specifically created to decrease TPS in dogs with CCL disease. This leads to a substantial decrease in cranial tibial subluxation, even though complete elimination of subluxation requires a specific surgical technique and angle of correction.2,3,10,a The TWO was created to correct caudal deformities of the proximal portion of the tibia and, since, has also been used to decrease TPS as an alternative to TPLO that may be technically simpler and not require a specific bone plate. However, scant information is available regarding the geometric and mechanical attributes of these surgeries.11,12,b

Closing wedge osteotomies may be performed by creating planar,9,13 curviplanar (dome),14 or V-shaped (chevron) kerfs. In humans, CWOs are used for phalangeal, ulnar, femoral, or tibial osteotomy stabilization, potentially because of their perceived increased stability over conventional closing wedge osteotomies.15–20 In 1 report,21 CWO healed faster than other wedge osteotomies, but it did not have clear advantages over other surgical methods in a recent review.22

Hinged circular ESF is a form of fixation widely used in humans to perform progressive corrective osteotomies of the proximal portion of the tibia. It is used as a less invasive alternative to internal fixation.23 Hinged circular ESF has been used to treat angular limb deformities and, in our teaching hospital, to alter TPS of dogs with CCL disease using HHCEF to perform progressive corrective osteotomies.24 In recent years, hinged unilateral ESF use has increased in humans, being considered technically simpler and less invasive than HHCEF. Additionally, hinged unilateral ESF allows pin insertion parallel to articular surfaces with juxta-articular osteotomies without additional components.25,26 A hinged unilateral ESF frame (ie, WOLF) has recently been designed by 1 author (DJM) and other investigators for correction of juxta-articular bone deformities, potentially including progressive alteration of TPS.

The purpose of the study reported here was to compare the geometric and mechanical properties of the following 5 canine tibial plateau leveling methods: TPLO,8 TWO,9 CWO, HHCEF, and WOLF. Properties evaluated included application time, accuracy of TPS correction, presence and magnitude of rotational and angular deformities, and axial stiffness of bone-implant constructs. We hypothesized that ESF would lead to a more rapid application and a more accurate and stable TPS correction, compared with internal fixation methods. We hypothesized that CWO would result in greater axial stiffness of bone-implant constructs than other internal fixation methods. We also hypothesized that ESF frame stiffness would not be negatively influenced by frame reuse.

Materials and Methods

Bone models—Tibial replicas from a 6-year-old male castrated Labrador Retriever with CCL disease and a TPS of 29° were created by use of rapid prototyping methods.27 A helical computed tomography scanc of the distal portion of the right thigh, crus, and pes was performed under sedation with medetomidine (5 μg/kg, IV) and hydromorphone (0.05 mg/kg, IV). One-millimeter-thick slices were generated through retrore-construction of 5-mm-thick slices. The tibia was reconstructed by use of 3-dimensional reconstruction softwared and bone models produced by stereolithography.e Raw data were then modified by use of software programs.f,g A base cylinder with equal diameter to the materials testing machine specimen holder was created and aligned with the tibial long axis. Blocksg were created representing menisci, and by use of a Boolean operation, exact features of the femoral condyles were replicated for future machining. Six prominences were cast (4 on the proximal portion of the tibia and 2 on the tibial shaft) to assess 3-dimensional orientation (TPS, rotation, and angulation) before and after corrective procedures (Figure 1). A first-generation model silicon mold was produced. The bone composite was devised by testing combinations of materials. Flexural modulus was compared between bone composites and cadaveric tibiae harvested from dogs euthanatized by IV administration of 1 mL/5 kg sodium pentobarbitalh for reasons other than this study. Cortical bone was reproduced by use of 2-component epoxy, bone powder, and glass fibers. Cancellous bone was reproduced by use of polyamine foam. Twenty-seven replicas were cast.

Figure 1—
Figure 1—

Craniocaudal (CC), mediolateral (ML), and proximodistal (PD) photographic views of a model of a canine tibia made by use of stereolithography (left panels) and the casting of that model made by use of 2-component epoxy, bone powder, and glass fibers (right panels). The models have prominences created for assessment of TPS, rotational malalignment, and mediolateral angulation. Rotational malalignment is measured by comparing AB and the central axis of the bolt placed through the model as seen from its proximal aspects. Mediolateral angulation is measured by comparing the direction of AB and CD. The TPS adjustment is measured by comparing the direction of EF and BG in the preoperative and final models.

Citation: American Journal of Veterinary Research 67, 4; 10.2460/ajvr.67.4.693

TPS measurement—The TPS was measured before surgery, after surgery (TPLO, TWO, and CWO), after adjustment (HHCEF and WOLF), and after mechanical testing (all methods). Bone models and constructs were digitally photographed from a distance of 1 m by use of a digital camera at the level of the stifle joint. Axes were drawn by image analysis software.i The TPS was measured by comparing the orientationof a line tangential with the discrete,canial portion of the medial tibial condyle to a line joining a point equidistant to the medial and lateral intercondylar tubercles, proximally, and a point equidistant to the cranial and caudal trochlear aspects of the talus, distally (Figure 1).28

TPLO—The proximal tibia underwent a TPLO with the use of a biradial 24-mm saw blade.12 Temporary reduction was achieved by a 1.6-mm-diameter Kirschner wire crossing the osteotomy. Six 3.5-mm cortical screwsj were tightened to 1.13 Nm with a factory-calibrated torque wrenchk; the 2 screws that were just proximal to the osteotomy site were placed in compression (Figure 2).29,30

Figure 2—
Figure 2—

Drawing of a tibia model during various stages of a TPLO. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-plate construct by 1°.

Citation: American Journal of Veterinary Research 67, 4; 10.2460/ajvr.67.4.693

TWO—The origin of angulation of the tibial plateau was defined as the intersection of a line perpendicular to the cranial-to-caudal midpoint of the medial tibial condyle and the anatomic axis (ie, TPS measurements).28 The anatomic axis was defined by a line joining the center of the trochlea of the talus and a point equidistant to the cranial and caudal aspects of the tibial shaft, 5 mm distal to the distal aspect of the tibial crest (Figure 3). An osteotomy was performed originating on the caudal aspect of the tibial shaft at a level corresponding to the intersection of the line perpendicular to the cranial-tocaudal midpoint of the medial tibial condyle and the anatomic axis. A second osteotomy was performed at a 24° angle to the former osteotomy intersecting on the caudal tibial cortex. All osteotomies, excluding the TPLO, were performed by use of an oscillating saw on an electric cordless drill.l Fully charged battery packs were interchanged between surgeries. Temporary reduction was achieved by a 1.6-mm-diameter Kirschner wire crossing the osteotomy in a cranioproximalto-caudodistal direction after wedge removal. A TWO bone platem was secured by use of seven 3.5-mm cortical screwsj torqued to 1.13 Nm; 2 screws that were just proximal and distal to the osteotomy site were placed in compression.29,30

Figure 3—
Figure 3—

Drawing of a tibia model with various stages of a TWO. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-plate construct by 3.8°.

Citation: American Journal of Veterinary Research 67, 4; 10.2460/ajvr.67.4.693

CWO—The chevron proximal and distal osteotomies were created with a custom-made 145° jig (Figure 4). In CWO, the osteotomy site in the caudal tibial cortex and plate fixation was identical to that of the TWO.

Figure 4—
Figure 4—

Drawing of a tibia model with various stages of a CWO. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-plate construct by 3.9°.

Citation: American Journal of Veterinary Research 67, 4; 10.2460/ajvr.67.4.693

HHCEF—The HHCEF frame was based on two 90-mm (inside diameter) stainless steel half-rings joined medially and laterally by 2 universal joints and cranially by an angular motor (Figure 5).n A 150-mm-long titanium rod° was secured medially on the distal ring by use of hemispheric washer fixation.31 Two transosseous wires and 2 half-pins (proximal ring), 1 transosseous wire and 1 half-pin (distal ring), and 4 half-pins (titanium rod) were used to secure the frame to the bone model. The wires were 1.5-mm-diameter Ilizarov wires,n and the half-pins were medium cortical interface pins with a 3.2-mm-diameter shaft and a 4-mm-diameter threaded portion.° Four small clampso connected half-pins to the titanium rod. Three small fixation clamp bolt-washer assemblies,o securing the half-pins to the half-rings, were torqued to 7 Nm. Wires were tensioned to 30 kg (294 N) with a new, factory-calibrated dynamometric wire tensioner.n Nuts for wire fixation were torqued to 7 Nm and other nuts to 3.5 Nm.31,32 The tibia underwent an osteotomy 10 mm distal to the tibial tubercle, and TPS was modified by adjusting the angular motor by an amount predetermined during preliminary testing.

Figure 5—
Figure 5—

Drawing of a tibia model with various stages of HHCEF. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-fixator construct by 4.9°.

Citation: American Journal of Veterinary Research 67, 4; 10.2460/ajvr.67.4.693

WOLF—The WOLF involved the use of a hinged linear ESF frame with a proximal T-clamp; midbody hinge joint; and central body hosting a sliding, longitudinal straight clamp (Figure 6). The WOLF frames were placed with the proximal clamp placed at a 24° angle in relation to the central body. The straight clamp translated within the central body by adjusting a self-locking 5-mm hex key cap screw with a 1-mm pitch, located at the most distal aspect of the fixator (Figure 6). Two 4-mm-diameter negative profile pinsn with a 3-mm core diameter, 4-mm outer diameter, and a transition zone in which thread height increased from 0 to 1 mm connected the proximal T-clamp to the proximal tibia. Two identical pins connected the longitudinal straight clamp to the tibial shaft with the midbody hinge joint centered at the tibial crest origin. Pinholes were predrilled by use of a custom 3-mm-diameter drill bit. Clamps were secured by torquing their 5-mm hex key cap screws to 15 Nm. An osteotomy was performed at the distal aspect of the tibial crest (Figure 6). The TPS was modified by distal clamp translation within the body by an amount predetermined during preliminary testing (Figure 6). The midbody hinge joint was then locked by torquing the 6-mm hex key cap screw to 25 Nm.

Figure 6—
Figure 6—

Drawing of a tibia model with various stages of WOLF. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-fixator construct by 3.3°.

Citation: American Journal of Veterinary Research 67, 4; 10.2460/ajvr.67.4.693

The target TPS after correction was 5° for all methods. Both HHCEF and WOLF frames were preset at 24° and adjusted acutely to achieve the desired TPS correction. All implants (screws, plates, wires, pins, and fixator components) were new, washed, and steam sterilized prior to surgery.

Application time—Time required for all corrective procedures was recorded from the beginning of the corrective procedure to the end of component hand tightening. The time necessary to preassemble HHCEF frames and to adjust HHCEF and WOLF frames was not recorded. Final component tightening was performed immediately before mechanical testing. Individual constructs were weighed.

Geometric assessment—Bone models were digitally photographed to obtain craniocaudal, mediolateral, and proximodistal views before surgery, after surgery (TPLO, TWO, CWO), after adjustment (HHCEF and WOLF), and after mechanical testing (all methods). Image analysis softwareh was used to measure TPS and the presence and magnitude of rotational and angular deformities by use of the geometric markers.28 The theoretical tibial long axis shift was measured on bone model drawings that replicated the surgical methods (Figures 2–6). All measurements were performed in random order by 1 author (BEH).

Mechanical testing—A solid aluminum replica of the femoral condyles was machined by use of computer numerical control (ie, CNC machined) from previous computed tomography data, with a proximal coupling to a universal testing machine.p All tests were performed in random order with a crosshead speed of 5 mm/min with 3 preconditioning loads and data recorded on the fourth loading event. All models were axially loaded before surgery to 600 N (62 kg).33 Bone-plate constructs were axially loaded after surgery to 300 N (31 kg). Bone-ESF frame constructs were axially loaded after surgery and after adjustment to 300 N (31 kg). All loading events were recorded on a personal computer. Three individual TPLO, TWO, and CWO plate constructs were tested after surgery (9 tests). Three individual HHCEF and WOLF constructs were tested after surgery and after adjustment (12 tests). Wires and pins were removed, and ESF frames were tested 2 additional times with new steam-sterilized hardware (24 tests). Nondestructive testing was ensured by comparison of bone model size and load displacement curves after each loading event. Axial stiffness was calculated as a function of the terminal slope of the load displacement curve for bone models and constructs on the fourth loading event.

Statistical analysis—A randomized block design was used to determine orders of surgery, testing, and geometric assessment by use of randomization tables.34 Application time, geometric assessment, and axial stiffness were assessed for all plate constructs and for the initial use of ESF constructs (15 constructs). Application time and construct axial stiffness were assessed after 2 additional uses of the fixators to assess effects of ESF frame reuse (12 additional constructs). All criteria were compared within and among methods by use of an ANOVA with fixed effects.q Results were compared with target values (TPS, 5°; rotation, 0°; angulation, 0°) by use of a 2-way t test.r Values of P < 0.05 were considered significant.

Results

Frame and plate placement—Mean ± SD bone model axial stiffness was 871 ± 208 N/mm (Table 1). Bone model axial stiffness within methods did not differ from their mean (P = 0.883), and mean bone model axial stiffness did not differ among methods (P = 0.133 to 0.822). The mean ± SD construct weights were 140.2 ± 6.7 g, 139.4 ± 3.6 g, and 143.1 ± 4.6 g for plates and screws used in TPLO, TWO, and CWO, respectively, and were 441.1 ± 4.1 g and 359.7 ± 4.5 g for frames, wires, and pins used in HHCEF and WOLF, respectively. Application times within methods did not differ significantly (P = 0.184) from their mean, and mean application times were significantly (P < 0.001) more rapid for WOLF frames than for other methods (Table 2). Postoperative TPSs within methods did not differ significantly (P = 0.243) from their mean. Mean postoperative TPSs were significantly (P = 0.006 to 0.018) lower for HHCEF and WOLF than for internal fixation methods and did not differ significantly (P = 0.597 and 0.092) from the 5° target. Conversely, the use of TPLO, TWO, and CWO led to a TPS that was significantly (P = 0.030, 0.030, and 0.027, respectively) larger than the target. The tibial long axis shifted 1°, 3.8°, 3.9°, 4.9°, and 3.3° following TPLO, TWO, CWO, HHCEF, and WOLF, respectively; however, they were not compared statistically (Figures 2–6). Postoperative rotation within methods did not differ significantly (P = 0.504) from their mean, and mean postoperative rotation did not differ significantly among methods (P = 0.171 to 0.963) or from the 0° target (P = 0.080 to 0.779). Postoperative mediolateral angulation within methods did not differ significantly (P = 0.137) from their mean, but the use of CWO led to a mean postoperative mediolateral varus angulation that was significantly larger than that following TPLO (P = 0.020) and HHCEF (P = 0.018) and than that of our 0° target (P < 0.001).

Table 1—

Mean ± SD axial stiffness data of 5 tibial plateau leveling methods in which 3 bone models were tested once.
MethodBone model (N/mm)Postoperative (N/mm)Stiffness difference between postoperative and bone model (%)Final (N/mm*)Stiffness difference between final and postoperative (%)Stiffness difference between final and bone model (%)
TPLO876 ± 229a701 ± 270a−15 ± 45a701 ± 270aNA−15 ± 45a
TWO788 ± 115a642 ± 70a−18 ± 15a642 ± 70aNA−18 ± 15a
CWO1,042 ± 299a637 ± 111a−36 ± 21a637 ± 111aNA−36 ± 21a,b
HHCEF729 ± 131a732 ± 259a−1 ± 22a140 ± 24b−79 ± 6a−80 ± 6b
WOLF919 ± 210a529 ± 89a−39 ± 23a321 ± 81b−39 ± 7b−62 ± 17a,b
Mean871 ± 208NANANANANA

For TPLO, TWO, and CWO, the final stiffness is the postoperative stiffness; for HHCEF and WOLF, the final stiffness is the after-adjustment stiffness.

Values with different superscript letters within a column indicate significant (P < 0.05) differences among methods. NA = Not applicable.

Construct axial stiffness decreased by 15% to 36% after internal fixation and by 1% and 39% immediately after HHCEF and WOLF frame placement, with no significant (P = 0.137 to 0.922) difference between methods (Table 1). Construct axial stiffness did not differ significantly among internal fixation methods (P = 0.587 to 0.968) or between ESF methods after frame adjustment (P = 0.149); however, constructs built by use of internal fixation methods were significantly (P = 0.001 to 0.023) axially stiffer than constructs made by use of ESF methods after their adjustments. After HHCEF and WOLF adjustment, construct axial stiffness further decreased from postoperative axial stiffness by 79% and 39%, respectively. After adjustment, HHCEF and WOLF were 80% and 62% less stiff than bone models, respectively. The mean percent change in axial stiffness after adjustment for HHCEF did not differ significantly from that of WOLF and CWO (P = 0.426 and 0.073, respectively) but was significantly lower than that of TPLO and TWO (P = 0.016 and 0.019, respectively).

Table 2—

Mean ± SD frame weight, application time, and geometric assessment of 5 tibial plateau leveling methods in which 3 bone models were tested once.
MethodConstruct weight (g)Application time (min)Postoperative TPS (°)Postoperative rotation(°)*Postoperative Mediolateral angulation(°)*
TPLO140.2 ± 6.727 ± 2b,d9.3 ± 1.9†b−3.4 ± 1.8a−0.7 ± 2.6a
TWO139.4 ± 3.621 ± 1b,c9.3 ± 1.9†b−3.3 ± 5.3a−4.2 ± 5.3b
CWO143.1 ± 4.624 ± 1b,c8.9 ± 1.6†b−3.0 ± 2.6a−7.3 ± 0.2†b
HHCEF441.1 ± 4.126 ± 3b,d4.7 ± 1.7a0.3 ± 0.7a−0.5° ± 0.7a
WOLF359.7 ± 4.59 ± 3a5.3 ± 0.2a0.8 ± 4.2a−3.3° ± 4.0b
TargetNANA500

For rotational malalignment assessment, negative values indicate internal rotation; for mediolateral angulation assessment, negative values indicate varus deformity.

Significantly (P < 0.05) different from target value.

Values with different superscript letters within a column indicate significant (P < 0.05) differences among methods. See Table 1 for remainder of key.

However, mean percent change in axial stiffness after adjustment for WOLF did not differ significantly (P = 0.060 to 0.255) from other methods.

Repeated frame use—Bone model axial stiffness did not differ significantly (P = 0.071 to 0.971) among models for ESF frame reuse. The time necessary to preassemble HHCEF frames was not recorded. Application times of HHCEF frames were significantly (P = 0.001) more rapid for the second set (15 ± 2 minutes) than the first set (26 ± 3 minutes) but not for the third set (12 ± 2 minutes), compared with the second set (P = 0.079). Application times of WOLF frames did not differ significantly (P = 0.106) between the second (6 ± 0 minutes) and first set (9 ± 3 minutes) or between the third (6 ± 1 minutes) and second set (P = 0.944). The postoperative axial stiffness did not differ significantly between reuses for HHCEF (P = 0.284 and 0.519) and WOLF (P = 0.686 and 0.126). Similarly, the axial stiffness after adjustment did not differ significantly for HHCEF (P = 0.077 and 0.497) and WOLF (P = 0.440 and 0.288).

Discussion

The purpose of our study was to evaluate geometric and mechanical properties of 3 internal fixation methods and 2 ESF methods aimed at canine tibial plateau leveling. For our study, we created bone models by use of rapid prototyping methods. Rapid prototyping has been described as a precise and effective method for in vitro testing and comparison of biological models.35 These models had the advantages of being identical in size, shape, and texture to the canine tibia and to each other; having comparable flexural modulus to the canine tibia (2,572 MPa for the 17.8-mm-diameter bone model, 6,212 MPa for a 17.3-mm-diameter cadaveric canine tibia, and 1,379 for a 19.3-mm-diameter delrin rod in preliminary testing); having specific geometric markers; and of being customized to our materials testing machine.

Our study had several limitations. Mechanical testing, for logistic reasons, was limited to axial loading. Although axial loading is the most critical aspect of the mechanical assessment of ESF methods,36 it may not be as relevant for plate fixation methods. Adding mediolateral and craniocaudal bending would enhance our assessment of the relative mechanical properties of the 5 tibial plateau leveling methods evaluated in our study. Our study was conducted on bone models. Geometric and mechanical properties of these bones may have differed from the properties of canine bones, even though the strength and stiffness measured in the bone models were similar in magnitude to canine bones. Variability was present among bone models, potentially as a result of slight variation in model geometry, composition, and positioning within the materials testing machine. Variability present among bone models lowered the power of our statistical analyses (β = 0.052). This negatively impacted our ability to detect actual differences between bone model structural properties. Also, the presence of musculoskeletal soft tissues would likely alter the geometric and mechanical findings of our study and would lengthen application times. For example, in our experience, most angular deformities present after tibial plateau leveling tend to be valgus deformities, potentially as a consequence of the traction generated by muscles located on the lateral aspect of the crus. Increased soft tissue tension during progressive distractive correction and increase in stiffness of the regenerate bone would generate additional wire tension and influence the mechanical properties of bone-ESF frame constructs.37

All methods compared in our study appear to be acceptable for tibial plateau leveling. The CWO constructs did not differ significantly from the other internal fixation methods or either ESF method when expressed as a percent change in construct axial stiffness between final position and the bone model. This may have been the result of the consistent varus angulation present in CWO constructs or the result of the potential lack of precision resulting from the use of a jig that did not fully constrain the saw blade. A more precise jig would allow a more precise assessment of the relative stability of CWO constructs, compared with other constructs. Also, the more complex osteotomy of CWO would likely settle more than that of TWO when axially loaded. The chevron cut, however, would likely impart resistance to cranially or caudally directed forces and, potentially, torsional forces as a result of the osteotomy face geometry. Internal fixation methods resulted in greater axial stiffness of bone-implant constructs than ESF methods. This increased stiffness would be advantageous in the early postoperative period. The in vivo stiffness after progressive distraction of a hinged ESF frame would likely differ from the stiffness measured in our study because the tension present in soft tissues during progressive distraction is an important mechanical factor in the overall stiffness of the bone-frame construct.37 We have used frames identical to HHCEF frames used here and have found a low occurrence of mechanical failure (1 titanium rod breakage out of 35 frames) and satisfactory results in clinical patients. Use of WOLF was more rapid than other methods used in our study. The decrease in application times found with repeated use of HHCEF but not WOLF suggests that a steeper learning curve exists for the use of HHCEF, compared with WOLF.

The ESF methods were more precise than internal fixation methods to reach a specific TPS in our study. The lack of accuracy in final TPS orientation resulted in part from the fact that, with TWO and CWO, a tibial long axis shift occurs during correction and the bone wedge angle is not equal to TPS change. We were aware of the tibial long axis shift but decided not to decrease it by aligning the cranial cortices or offsetting the proximal and distal chevrons when planning and performing TWO and CWO. We considered that decreasing this tibial long axis shift would potentially negatively impact the mechanical properties of the constructs and would create constructs that differed significantly from the bone-plate constructs created in our clinical population treated with TWO and CWO. As an alternative, we could have increased the size of the osteotomy by approximately 5° to offset the tibial long axis shift and therefore increase the precision of the correction. Clinically, it would appear logical to increase the size of the osteotomy when performing a TWO or CWO or other procedure aimed at decreasing TPS to a specific target angle, because an undercorrection would likely lead to continued subluxation, as suggested in a recent abstract.a A similar shift in tibial long axis, albeit smaller in magnitude, also occurred with the use of TPLO. A tibial long axis shift also occurred with the use of HHCEF and WOLF, but the amount necessary to adjust TPS was predetermined during preliminary testing, and therefore the effects of that tibial long axis shift were corrected during adjustments. The tibial long axis shifts were measured on drawings of the 5 methods and not directly on each model. The lack of TPS accuracy may also have resulted from the fact that with plate fixation, the final TPS results directly from the shape of the bone wedge or the osteotomy sliding method occurring during surgery, but with ESF, the final TPS results from adjustments made to the frames after surgery. The lack of accuracy for TPLO in our study may have resulted from an underestimation of the magnitude of correction required to achieve a 5° postoperative TPS, from an osteotomy centered too cranially,10 or from an error in postoperative TPS measurements specific to TPLO. The methods tested did not appear to lead to the creation of rotational deformities. Varus angulation was present after CWO and, to a lesser extent, after TWO and WOLF. Overall, the geometric alterations created by these corrective methods were minor.

In conclusion, the 5 tibial plateau leveling methods evaluated in vitro in our study had acceptable geometric and mechanical properties. Constructs built by use of internal fixation methods were axially stiffer than constructs built by use of ESF methods and adjusted. Larger in vitro or clinical studies will be advantageous to compare specific in vivo advantages of particular TPS adjustment methods.

ABBREVIATIONS

CCL

Cranial cruciate ligament
TPS

Tibial plateau slope
TPLO

Tibial plateau leveling osteotomy
TWO

Tibial wedge osteotomy
CWO

Chevron wedge osteotomy
ESF

External skeletal fixation
HHCEF

Hinged hybrid circular external fixation
WOLF

Wedge osteotomy linear fixation
Nm

Newton-meters
a.

Kowaleski MP, Apelt D, Mattoon JS, et al. Effect of tibial plateau leveling osteotomy position on cranial tibial subluxation (abstr), in Proceedings. 31st Conf Vet Orthop Soc 2004;39.

b.

Bailey CJ, Smith BA, Black AP. Geometric implications of tibial wedge osteotomies (abstr), in Proceedings. 30th Conf Vet Orthop Soc 2003;60.

c.

CT Sytec SRi, General Electric Co, Fairfield, Conn.

d.

Mimics, version 7.10, Materialise, Leuven, Belgium.

e.

SLA-190, 3-D Systems, Valencia, Calif.

f.

Geomagic Studio, version 6.0, Raindrop Geomagic, Research Triangle Park, NC.

g.

V2003-2004, SolidWorks Corp, Concord, Mass.

h.

Beuthanasia-D, Schering-Plough Animal Health, Summit, NJ.

i.

Adobe Photoshop, version 5.0, Adobe Systems Inc, Mountain View, Calif.

j.

Synthes Ltd, Paoli, Pa.

k.

Sturtevant Richmont, Franklin Park, Ill.

l.

Stryker II, Stryker Instruments Inc, Kalamazoo, Mich.

m.

Jorgensen Laboratories Inc, Loveland, Colo.

n.

Hofmann S.r.L., Monza, Italy.

o.

SK External Skeletal Fixation System, IMEX Inc, Longview, Tex.

p.

ATS 1605C, Applied Test Systems, Inc., Butler, Pa.

q.

PROC GLM, SAS, version 8.02, SAS Institute Inc, Cary, NC.

r.

JMP, version 5.0.1.2, SAS Institute Inc, Cary, NC.

  • 1↑

    Pond MJ, Campbell JR. The canine stifle joint. I. Rupture of the anterior cruciate ligament. An assessment of conservative and surgical treatment. J Small Anim Pract 1972; 13: 1–10.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2↑

    Reif U, Hulse DA, Hauptman JG. Effect of tibial plateau leveling on stability of the canine cranial cruciate-deficient stifle joint: an in vitro study. Vet Surg 2002; 31: 147–154.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3↑

    Warzee CC, Dejardin LM, Arnoczky SP, et al. Effect of tibial plateau leveling on cranial and caudal tibial thrusts in canine cranial cruciate-deficient stifles: an in vitro experimental study. Vet Surg 2001; 30: 278–286.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4

    Morris E, Lipowitz AJ. Comparison of tibial plateau angles in dogs with and without cranial cruciate ligament injuries. J Am Vet Med Assoc 2001; 218: 363–366.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5

    Reif U, Probst CW. Comparison of tibial plateau angles in normal and cranial cruciate deficient stifles of Labrador retrievers. Vet Surg 2003; 32: 385–389.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6↑

    Korvick D, Pijanowski G, Schaeffer D. Three-dimensional kinematics of the intact and cranial cruciate ligament-deficient stifle of dogs. J Biomech 1994; 27: 77–87.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7

    Slocum B, Devine T. Cranial tibial wedge osteotomy: a technique for eliminating cranial tibial thrust in cranial cruciate ligament repair. J Am Vet Med Assoc 1984; 184: 564–569.

    • Search Google Scholar
    • Export Citation
  • 8↑

    Slocum B, Slocum TD. Tibial plateau leveling osteotomy for repair of cranial cruciate ligament rupture in the canine. Vet Clin North Am Small Anim Pract 1993; 23: 777–795.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9↑

    Watt P. Tibial plateau levelling. Aust Vet J 2000; 78: 385–386.

  • 10↑

    Kowaleski MP, McCarthy RJ. Geometric analysis evaluating the effect of tibial plateau leveling osteotomy position on postoperative tibial plateau slope. Vet Comp Orthop Traumatol 2004; 17: 30–34.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11

    Wheeler JL, Cross AR, Gingrich W. In vitro effects of osteotomy angle and osteotomy reduction on tibial angulation and rotation during the tibial plateau-leveling osteotomy procedure. Vet Surg 2003; 32: 371–377.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12↑

    Slocum B, Slocum TD. Tibial plateau leveling osteotomy technique, in Proceedings. Slocum Enterprises Tibial Plateau Leveling Osteotomy Course 1999; 4–7.

    • Search Google Scholar
    • Export Citation
  • 13

    Selmi A, Padilha FJ. Rupture of the cranial cruciate ligament associated with deformity of the proximal tibia in five dogs. J Small Anim Pract 2001; 42: 390–393.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14↑

    MacDonald JM, Matthiesen D. Treatment of forelimb growth plate deformity in 11 dogs by radial dome osteotomy and external coaptation. Vet Surg 1991; 20: 402–408.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15

    Lewis RJ, Feffer HL. Modified chevron osteotomy of the first metatarsal. Clin Orthop Relat Res 1981; 157: 105–109.

  • 16

    Austin DW, Leventen EO. A new osteotomy for hallux valgus: a horizontally directed “V” displacement osteotomy of the metatarsal head for hallux valgus and primus varus. Clin Orthop Relat Res 1981; 157: 25–30.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17

    Petraco DM, Koval KJ, Kummer FJ, et al. Fixation stability of olecranon osteotomies. Clin Orthop Relat Res 1996; 333: 181–185.

  • 18

    Chareancholvanich K, Becker DA, Gustilo RB. Treatment of congenital dislocated hip by arthroplasty with femoral shortening. Clin Orthop Relat Res 1999; 360: 127–135.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19

    Marcus RE, Balourdas GM, Heiple KG. Ankle arthrodesis by chevron fusion with internal fixation and bone-grafting. J Bone Joint Surg Am 1983; 65: 833–838.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 20

    Berry DJ, Muller ME. Chevron osteotomy and single wire reattachment of the greater trochanter in primary and revision total hip arthroplasty. Clin Orthop Relat Res 1993; 294: 155–161.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 21↑

    Easley ME, Kiebzak GM, Davis WH, et al. Prospective, randomized comparison of proximal crescentic and proximal chevron osteotomies for correction of hallux valgus deformity. Foot Ankle Int 1996; 17: 307–316.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 22↑

    Ferrari J, Higgins JP, Prior TD. Interventions for treating hallux valgus (abductovalgus) and bunions. Cochrane Database Syst Rev www.mrw.interscience.wiley.com/cochrane/clsysrev/articles/CD000964frame.htmlAccessed Jul 1, 2005.

    • Search Google Scholar
    • Export Citation
  • 23↑

    Herzenberg JE, Waanders NA. Calculating rate and duration of distraction for deformity correction with the Ilizarov technique. Orthop Clin North Am 1991; 22: 601–611.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 24↑

    Marcellin-Little DJ, Ferretti A, Roe SC, et al. Hinged Ilizarov external fixation for correction of antebrachial deformities. Vet Surg 1998; 27: 231–245.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25

    Hammer R. A new device for external fixation. Acta Orthop Scand 1988; 59: 708–711.

  • 26

    Mollica Q, Leonardi W, Travaglianti G. Correction of lower limb deformity using external fixation. Ital J Orthop Traumatol 1992; 18: 297–302.

    • Search Google Scholar
    • Export Citation
  • 27↑

    Potamianos P, Amis AA, Forester AJ, et al. Rapid prototyping for orthopaedic surgery. Proc Inst Mech Eng [H] 1998; 212: 383–393.

  • 28↑

    Baroni E, Matthias RR, Marcellin-Little DJ, et al. Comparison of radiographic assessments of the tibial plateau slope in dogs. Am J Vet Res 2003; 64: 586–589.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 29

    Collinge C, Stern S, Cordes S, et al. Mechanical properties of small fragment screws. Clin Orthop Relat Res 2000; 373: 277–284.

  • 30

    Blake A. Threaded fasteners material and design. New York: Marcel Dekker Inc, 1986.

  • 31↑

    Marcellin-Little DJ, Roe SC, Rovesti GL, et al. Are circular external fixators weakened by the use of hemispheric washers? Vet Surg 2002; 31: 367–374.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 32

    Wosar MA, Marcellin-Little DJ, Roe SC. Influence of bolt tightening torque, wire size, and component reuse on wire fixation in circular external fixation. Vet Surg 2002; 31: 571–576.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 33↑

    Budsberg SC, Verstraete MC, Soutas-Little RW. Force plate analysis of the walking gait in healthy dogs. Am J Vet Res 1987; 48: 915–918.

    • Search Google Scholar
    • Export Citation
  • 34↑

    Snedecor GW, Cochran WG. Statistical methods. 7th ed. Ames, Iowa: Iowa State University Press, 1980.

  • 35↑

    Webb PA. A review of rapid prototyping (RP) techniques in the medical and biomedical sector. J Med Eng Technol 2000; 24: 149–153.

  • 36↑

    Fleming B, Paley D, Kristiansen T, et al. A biomechanical analysis of the Ilizarov external fixator. Clin Orthop Relat Res 1989; 241: 95–105.

    • Search Google Scholar
    • Export Citation
  • 37↑

    Lewis DD, Bronson DG, Samchukov ML, et al. Biomechanics of circular external skeletal fixation. Vet Surg 1998; 27: 454–464.

Contributor Notes

Dr. Hildreth's present address is the Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

Dr. Hildreth was partially supported by a Merck-Merial training scholarship.

Presented in part at the 2004 American College of Veterinary Surgeons Surgical Summit, Denver, CO.

The authors would like to thank Bonnie DeYoung and Ketan Jajal and Drs. Denis R. Cormier, Harvey A. West II, and Peter Sebestyen for technical assistance; Dr. Jason Osborne, Janet Bartz, and Matthew Gribbin for statistical consultation; Brenda Bunch for illustrations; and Dr. Joachim Pfeil and Wolfgang Veith for assistance in WOLF frame design.

Dr. Marcellin-Little.
Cover American Journal of Veterinary Research
American Journal of Veterinary Research
Publication Date:
01 Apr 2006
  • Figure 1—
    View in gallery
    Figure 1—

    Craniocaudal (CC), mediolateral (ML), and proximodistal (PD) photographic views of a model of a canine tibia made by use of stereolithography (left panels) and the casting of that model made by use of 2-component epoxy, bone powder, and glass fibers (right panels). The models have prominences created for assessment of TPS, rotational malalignment, and mediolateral angulation. Rotational malalignment is measured by comparing AB and the central axis of the bolt placed through the model as seen from its proximal aspects. Mediolateral angulation is measured by comparing the direction of AB and CD. The TPS adjustment is measured by comparing the direction of EF and BG in the preoperative and final models.

  • Figure 2—
    View in gallery
    Figure 2—

    Drawing of a tibia model during various stages of a TPLO. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-plate construct by 1°.

  • Figure 3—
    View in gallery
    Figure 3—

    Drawing of a tibia model with various stages of a TWO. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-plate construct by 3.8°.

  • Figure 4—
    View in gallery
    Figure 4—

    Drawing of a tibia model with various stages of a CWO. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-plate construct by 3.9°.

  • Figure 5—
    View in gallery
    Figure 5—

    Drawing of a tibia model with various stages of HHCEF. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-fixator construct by 4.9°.

  • Figure 6—
    View in gallery
    Figure 6—

    Drawing of a tibia model with various stages of WOLF. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-fixator construct by 3.3°.

Figure 1—

Craniocaudal (CC), mediolateral (ML), and proximodistal (PD) photographic views of a model of a canine tibia made by use of stereolithography (left panels) and the casting of that model made by use of 2-component epoxy, bone powder, and glass fibers (right panels). The models have prominences created for assessment of TPS, rotational malalignment, and mediolateral angulation. Rotational malalignment is measured by comparing AB and the central axis of the bolt placed through the model as seen from its proximal aspects. Mediolateral angulation is measured by comparing the direction of AB and CD. The TPS adjustment is measured by comparing the direction of EF and BG in the preoperative and final models.
Figure 2—

Drawing of a tibia model during various stages of a TPLO. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-plate construct by 1°.
Figure 3—

Drawing of a tibia model with various stages of a TWO. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-plate construct by 3.8°.
Figure 4—

Drawing of a tibia model with various stages of a CWO. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-plate construct by 3.9°.
Figure 5—

Drawing of a tibia model with various stages of HHCEF. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-fixator construct by 4.9°.
Figure 6—

Drawing of a tibia model with various stages of WOLF. Notice the tibial long axis shift (middle panel). The corrective osteotomy cranially displaces the tibial long axis of the bone-fixator construct by 3.3°.
  • 1

    Pond MJ, Campbell JR. The canine stifle joint. I. Rupture of the anterior cruciate ligament. An assessment of conservative and surgical treatment. J Small Anim Pract 1972; 13: 1–10.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2

    Reif U, Hulse DA, Hauptman JG. Effect of tibial plateau leveling on stability of the canine cranial cruciate-deficient stifle joint: an in vitro study. Vet Surg 2002; 31: 147–154.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3

    Warzee CC, Dejardin LM, Arnoczky SP, et al. Effect of tibial plateau leveling on cranial and caudal tibial thrusts in canine cranial cruciate-deficient stifles: an in vitro experimental study. Vet Surg 2001; 30: 278–286.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4

    Morris E, Lipowitz AJ. Comparison of tibial plateau angles in dogs with and without cranial cruciate ligament injuries. J Am Vet Med Assoc 2001; 218: 363–366.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5

    Reif U, Probst CW. Comparison of tibial plateau angles in normal and cranial cruciate deficient stifles of Labrador retrievers. Vet Surg 2003; 32: 385–389.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6

    Korvick D, Pijanowski G, Schaeffer D. Three-dimensional kinematics of the intact and cranial cruciate ligament-deficient stifle of dogs. J Biomech 1994; 27: 77–87.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7

    Slocum B, Devine T. Cranial tibial wedge osteotomy: a technique for eliminating cranial tibial thrust in cranial cruciate ligament repair. J Am Vet Med Assoc 1984; 184: 564–569.

    • Search Google Scholar
    • Export Citation
  • 8

    Slocum B, Slocum TD. Tibial plateau leveling osteotomy for repair of cranial cruciate ligament rupture in the canine. Vet Clin North Am Small Anim Pract 1993; 23: 777–795.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9

    Watt P. Tibial plateau levelling. Aust Vet J 2000; 78: 385–386.

  • 10

    Kowaleski MP, McCarthy RJ. Geometric analysis evaluating the effect of tibial plateau leveling osteotomy position on postoperative tibial plateau slope. Vet Comp Orthop Traumatol 2004; 17: 30–34.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11

    Wheeler JL, Cross AR, Gingrich W. In vitro effects of osteotomy angle and osteotomy reduction on tibial angulation and rotation during the tibial plateau-leveling osteotomy procedure. Vet Surg 2003; 32: 371–377.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12

    Slocum B, Slocum TD. Tibial plateau leveling osteotomy technique, in Proceedings. Slocum Enterprises Tibial Plateau Leveling Osteotomy Course 1999; 4–7.

    • Search Google Scholar
    • Export Citation
  • 13

    Selmi A, Padilha FJ. Rupture of the cranial cruciate ligament associated with deformity of the proximal tibia in five dogs. J Small Anim Pract 2001; 42: 390–393.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14

    MacDonald JM, Matthiesen D. Treatment of forelimb growth plate deformity in 11 dogs by radial dome osteotomy and external coaptation. Vet Surg 1991; 20: 402–408.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15

    Lewis RJ, Feffer HL. Modified chevron osteotomy of the first metatarsal. Clin Orthop Relat Res 1981; 157: 105–109.

  • 16

    Austin DW, Leventen EO. A new osteotomy for hallux valgus: a horizontally directed “V” displacement osteotomy of the metatarsal head for hallux valgus and primus varus. Clin Orthop Relat Res 1981; 157: 25–30.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17

    Petraco DM, Koval KJ, Kummer FJ, et al. Fixation stability of olecranon osteotomies. Clin Orthop Relat Res 1996; 333: 181–185.

  • 18

    Chareancholvanich K, Becker DA, Gustilo RB. Treatment of congenital dislocated hip by arthroplasty with femoral shortening. Clin Orthop Relat Res 1999; 360: 127–135.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19

    Marcus RE, Balourdas GM, Heiple KG. Ankle arthrodesis by chevron fusion with internal fixation and bone-grafting. J Bone Joint Surg Am 1983; 65: 833–838.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 20

    Berry DJ, Muller ME. Chevron osteotomy and single wire reattachment of the greater trochanter in primary and revision total hip arthroplasty. Clin Orthop Relat Res 1993; 294: 155–161.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 21

    Easley ME, Kiebzak GM, Davis WH, et al. Prospective, randomized comparison of proximal crescentic and proximal chevron osteotomies for correction of hallux valgus deformity. Foot Ankle Int 1996; 17: 307–316.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 22

    Ferrari J, Higgins JP, Prior TD. Interventions for treating hallux valgus (abductovalgus) and bunions. Cochrane Database Syst Rev www.mrw.interscience.wiley.com/cochrane/clsysrev/articles/CD000964frame.htmlAccessed Jul 1, 2005.

    • Search Google Scholar
    • Export Citation
  • 23

    Herzenberg JE, Waanders NA. Calculating rate and duration of distraction for deformity correction with the Ilizarov technique. Orthop Clin North Am 1991; 22: 601–611.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 24

    Marcellin-Little DJ, Ferretti A, Roe SC, et al. Hinged Ilizarov external fixation for correction of antebrachial deformities. Vet Surg 1998; 27: 231–245.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25

    Hammer R. A new device for external fixation. Acta Orthop Scand 1988; 59: 708–711.

  • 26

    Mollica Q, Leonardi W, Travaglianti G. Correction of lower limb deformity using external fixation. Ital J Orthop Traumatol 1992; 18: 297–302.

    • Search Google Scholar
    • Export Citation
  • 27

    Potamianos P, Amis AA, Forester AJ, et al. Rapid prototyping for orthopaedic surgery. Proc Inst Mech Eng [H] 1998; 212: 383–393.

  • 28

    Baroni E, Matthias RR, Marcellin-Little DJ, et al. Comparison of radiographic assessments of the tibial plateau slope in dogs. Am J Vet Res 2003; 64: 586–589.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 29

    Collinge C, Stern S, Cordes S, et al. Mechanical properties of small fragment screws. Clin Orthop Relat Res 2000; 373: 277–284.

  • 30

    Blake A. Threaded fasteners material and design. New York: Marcel Dekker Inc, 1986.

  • 31

    Marcellin-Little DJ, Roe SC, Rovesti GL, et al. Are circular external fixators weakened by the use of hemispheric washers? Vet Surg 2002; 31: 367–374.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 32

    Wosar MA, Marcellin-Little DJ, Roe SC. Influence of bolt tightening torque, wire size, and component reuse on wire fixation in circular external fixation. Vet Surg 2002; 31: 571–576.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 33

    Budsberg SC, Verstraete MC, Soutas-Little RW. Force plate analysis of the walking gait in healthy dogs. Am J Vet Res 1987; 48: 915–918.

    • Search Google Scholar
    • Export Citation
  • 34

    Snedecor GW, Cochran WG. Statistical methods. 7th ed. Ames, Iowa: Iowa State University Press, 1980.

  • 35

    Webb PA. A review of rapid prototyping (RP) techniques in the medical and biomedical sector. J Med Eng Technol 2000; 24: 149–153.

  • 36

    Fleming B, Paley D, Kristiansen T, et al. A biomechanical analysis of the Ilizarov external fixator. Clin Orthop Relat Res 1989; 241: 95–105.

    • Search Google Scholar
    • Export Citation
  • 37

    Lewis DD, Bronson DG, Samchukov ML, et al. Biomechanics of circular external skeletal fixation. Vet Surg 1998; 27: 454–464.

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